In the very upperleft corner of your standard tools pallet is a little square drawn from a dashed line. If you click on it and hold the mouse done, several other shapes will slide out from it. Pick one of those. Then you can double click on the tool you've selected and it will pop up a pallet for that tool, you can set aspect ratio's and sizes with it. Then, draw a shape selection on your canvas. If you right click on it you'll have options to fill and stroke etc... You can also use the paintbucket to fill it. Look on the adobe help menu, they've got some decent help files.